Stroke is the leading cause of serious disability in the U.S. While the neuroprotective power of hypothermia has been known decades, our ability to fully harness its protective power has not come easily. The objective of this project is to develop a cooling catheter that can rapidly cool the brain. Existing cooling catheters cool systemically. As a result, 2 factors reduce the effectiveness of hypothermia: 1) the thermal inertia of the whole body delays the time to target temperatures, and 2) the target temperatures are warmer than optimal temperatures because of cardiovascular and infection concerns. Our innovative technology explores another heat transfer augmentation technique that has not been explored: active mixing. Using dynamic heat exchange surfaces instead of static or motionless ones, we intend to create a catheter that meets the necessary cooling requirements while still maintaining adequate blood perfusion. Assuming 20% of U.S. stroke victims are open to hypothermia treatment, the anticipated market for these prototypes is $120-180 million dollars. The specific aims of our Phase I feasibility project are the following: 1) design and build 2 cooling catheter prototypes for in vitro and in vivo testing, 2) test and evaluate the in vitro performance of the prototypes, and 3) test and evaluate the in vivo performance and safety, in terms of vessel damage & hemocompatability. Using a first order heat transfer model and an existing carotid artery hemodynamic model, designs will be transformed into 3D solids and manufactured. In vitro testing will follow on a bench with demonstrated energy balance accuracy. Promising in vitro prototypes will then be used in a pilot animal study to demonstrate feasibility in terms of safety and performance in a large animal. Device performance will be gauged by 3 factors: its ability to cool, its ability to not obstruct blood flow, and its ability to operate safely.